Many diverse types of systems need to remotely determine the position of various objects or elements within them. For example, maritime, airborne, and land-bound entities use positioning information for navigational and other purposes. Communications systems, whether land-line telecommunication or cellular telecommunication, require location information to accurately route information from a data source to its destination. Accurate location information improves system safety, reliability, and efficiency. In the case of cellular telecommunications, accurate location information allows the system to efficiently route data to user terminals.
Cellular telecommunications systems use location information to route data to specific zones or cells of a system where a specific user terminal is known to exist. This partitioning of the system allows data delivery to specific cells within a system and does not require unnecessary consumption of system bandwidth in cells where the user terminal is not resident.
Positioning systems exist that utilize multiple satellites. Many of these, such as U.S. Pat. No. 4,445,118 to Taylor et al., utilize triangulation techniques but suffer limitations in that they require multiple satellites for position calculations. In other positioning systems, such as U.S. Pat. No. 4,819,053 to Halavais, a satellite with a scanning narrow beamwidth antenna looks for detectable transmissions from user terminals, but such systems place a considerable power burden on the transmitting user terminal.
The above-described prior art configurations could provide satisfactory positioning under some but not all, circumstances. In a global satellite communication system, known solutions would generally fail to deliver adequate geolocation at a reasonable price.
Thus, there is a significant need for an improved self-geolocation system for user terminals operating within a satellite cellular communication system.